Smoothing a bathroom wall for painting after removing tile.

Last night I began to take down the old, poorly done tile in my bathroom. The woman in me was expecting to see a pretty wall with a little bit of leftover adhesive that could be scraped away. That was not the case. The wall is not smooth and ready for primer and paint. It has a hole near one of the fixtures and has a few gals inbetween what looks like cardboard boards. Is there something I can lay over the wall to fill in the gaps and prepare it for paint and retiling?